Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
PA-~2 ~ 117Z559
SOLUTION MINING OF AN INCLINED STRUCTURE
BACKGROUND OF THE INVENTION
Heretofore it has been generally conceded by those
skilled in the art of solution mining of sylvinite deposits
that only thick beds, in essentially flat deposits, could be
solution mined economically. In prior solution mining, an oil
blanket, air blanket or some other such material had to be
maintained on the top of the solution mining liquid in the ore
cavity in order to avoid dissolution of the salt (NaCl) layer
above the ore being mined.
In prior solution mining techniques, the width of the
cavity developed by one or a plurality of wells was limited by
the stability of the cavity roof and the fact that as the
active dissolution face moved farther from the inlet, the
major portion of the unsaturated solution was farther removed
from contact with the active dissolution area, and solution
activity in relation to cavity size decreased.
Exemplary of the prior art technology is the method
described in U.S. Patent 3,341,252 (Dahms et al.) entitled
"Solution Mining of Sloping Strata". In this patent the method
involves drilling a plurality of bore holes spaced in both the
directions of the dip and in the direction of the strike in a
sloping stratum, and communication is developed among the bore
holes in the direction of the strike, but intentionally
avoided in the direction of the dip. The patented technique
recognizes prior art knowledge that otherwise inert pro-
tective layers of nonsolvent material such as hydrocarbon oil
would be required to prevent vertical extraction in the
cavity.
In U.S. Patent 3,442,553 (Kutz) entitled "Slurry
Mining of Carnallite", a method is described for slurry mining
of double salts with specific reference to carnallite, which
contains potassium chloride and magnesium chloride. In order
for the method to work, it is necessary to have a steeply
sloping bed containing double salts which form incongruently
saturated solutions. The less soluble salt (potassium chlo-
ride) is left as a slurry in the bottom of the cavity. The less
soluble salt is then removed as a slurry entrained by a
saturated or nearly saturated solution of the more soluble
salt.
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SUMMARY OF THE INVENTION
The present invention provides a method for solution
mining of a relatively thin extractable ore stratum in the
direction upwardly of a moderately or steeply inclined struc-
ture. It is not necessary with this method to ~aintain an
inert nonsolvent protective layer at the top of the cavity
since the overlying stratum is composed of nonsoluble mate-
rial. The method also allows dissolution of beds containing
single salts or multiple salts. It comprises establishing a
bore hole communicating with the ore stratum and injecting
water into the bore hole such that the dissolution of the
active mining face moves upwardly just under the insoluble
stratum in the updip direction and away from the bore hole.
The incoming water flows in the updip direction along the top
of the cavity to insure that the fresh water is rapidly and
continuously delivered to the active mining face in the
cavity.
Solution mining method particularly adapted for
recovery of potash and the like from relatively thin, inclined
strata at substantial depths and involving the dissolution of
ore strata, overlain by insoluble strata, while leaving the
remainder of the formation in place. Water is injected down
a bore hole at a predetermined rate and, being much less dense
than present brine, flows in an updip direction along the
top of the cavity to a forward mining face remote from the
drill hole. Loaded, heavy brine flows downdip along the
bottom of the stratum to an outflow pipe communicating with
the bottom of the bore hole.
DESCRIPTION OF THE DRAWINGS
Figure 1 is a schematic diagram in profile of a cavity
being mined in accordance with the methods of the present
invention.
Figure 2 is an isometric schematic diagram con-
sistent with Figure 1~
Figure 3 is an isometric schematic diagram con-
sistent with Figure 1 showing the extension of the system to
a multi ell operation.
1172559
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to the drawings, a typical inclined ore
formation is shown as to which the method of the present
invention is particularly adapted. The formation shown is
exemplary of the saline deposits of the Paradox Basin in
southeast Utah. Although the rich deposits of potash (KCl)
in that area have been known for many years, no economical way
of exploiting them had been developed heretofore. One mine
based on the conventional room-pillar method of mining was
operated for some time but was discontinued due to excessive
mining costs. Prior to the present invention, little thought
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had been given to solution mining in the Paradox Basin area
due to the inclined and distorted nature of the deposits. The
present invention, as will be described more fully below,
takes advantage of this inclined orientation and insoluble
zoning to develop an effective and efficient mining system,
even in spite of the fact that some of the mineralization of
interest is below 7,000 feet.
The primary salt of interest is sylvinite
(KCl.NaCl). The method is, however, applicable to any
soluble material bounded by an overlying insoluble zone.
In the formation shown in the drawings, the extract-
able ore layer 10 is located at a substantial depth below
ground level 11 and slopes upwardly in the dip direction, i.e.
from right to left as viewed in the drawings, and as indicated
by Arrow A. The strike direction, i.e. at a right angle to
the dip direction, is indicated by Arrow B.
Immediately above the ore zone or layer 10 is an
impermeable and insoluble layer 12 of shale, dolomite,
anhydrite or the like, and immediately below the ore layer 10
is a salt layer 13 (NaCl). The layer of salt 13 below the ore
layer is not critical to the patented process.
Drill hole 14 extends vertically downward from
ground level and initially through ore layer 10 and partially
into the underlying salt layer to form a sump 20 for the
effluent, as will be described hereinafter. Fresh water pipe
15 extends down bore hole 14 and terminates at its lower end
17 near the upper portion or top 18 of ore layer 10. Exit pipe
16 is concentrically disposed within inlet water pipe 15 and
extends downwardly to a terminal point 19 adjacent the sump
20 in salt layer 13.
In operation fresh water is injected into the mining
cavity 21 through pipe 15 and is discharged and flows along
the top 18 of the cavity 21 in the direction of Arrow C, i.e.
upwardly in the updip direction, into contact with and out-
wardly and downwardly along the active mining face 22 as
indicated by Arrow D and as shown in Figure 2. In practice,
the solution mining system can operate with water injection
down the tubing 16 and brine extraction up the annulus. As
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shown, the dissolution area or mining face 22 may form a
widening arc updip from the drill hole 14. The loaded brine
flows downdip along the top 23 of the underlying salt layer
13 in the direction of arrows, into sump 20 and then exits
through discharge pipe 16 for further extractive processing
by conventional methods such as solar evaporation, standard
evaporative crystallizers, etc.
Figure 3 shows the layout as the solution mining
process is expanded. This shows injection wells 24 and 25.
By moving the injection of fresh water closer to the mining
face, the mixing action of the water with the brine is
reduced, thereby delivering almost pure water to the dis-
solution area. This increases the rate of solution, spreads
the dissolution area laterally, and increases the ore-water
contact area by forming a scalloped-shaped interface 27.
When the cavity expanse becomes too large for roof stability,
the pressure in the cavity can be increased to provide
adequate support.
Although not shown in drawings, any number of ini-
tial wells can be developed along the base or side of an
inclined structure. The number depends on the mining plan and
economic factors.
Extraction under normal operating conditions will
be from wells with sumps that are in the lowest part of the
solution mining complex, as the brines with the highest
densities will migrate to these areas.
The thickness and composition of the stratum ex-
tracted controls or determines the injection and extraction
rate of the solute. If the rate is too rapid, too much salt
from the floor 23 will be dissolved. If the rate is too slow,
a thin stratum just under the insoluble layer 12 will be
dissolved, and important mineral values will be left on the
floor.
Normally the method of the invention will operate at
ambient or formation temperature, although heat may be added
if desired.
The KCl content of sylvinite mineral zones mined
will usually be above about 15~ KCl, although there is no
upper or lower limit of enrichment that may be mined with the
present process.
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While one embodiment of the present invention has
been shown and described herein, it is to be understood that
certain changes and/or additions may be made thereto by those
skilled in the art withoutdeparting from the scope and spirit
of the invention.
